EDEN PRAIRIE, Minn. (AP) The Vikings' seemingly constant search for long-term success and stability at quarterback took another turn on Wednesday.

Sam Bradford's future was cast in further doubt because of another knee surgery.

And Teddy Bridgewater finally made his way back to the active roster from his devastating knee injury.

Meanwhile, coach Mike Zimmer announced Case Keenum will make his seventh start of the season for the game at Washington on Sunday.

"Case has done great," Zimmer said. "So we just keep going from there and see how this thing plays out."

The Vikings (6-2) activated Bridgewater from the physically unable to perform list, adding him to the active roster for the first time in more than 14 months since his left knee was dislocated during practice. The freak injury resulted in ligament tears and an ambulance ride to the emergency room to save his leg.

The Vikings faced a deadline on Wednesday at the end of the three-week window that opened when Bridgewater resumed practice with the team.

To make room on the 53-man roster, Bradford was placed on injured reserve after having arthroscopic surgery the day before on his left knee, which had ACL tears in 2013 and 2014.

Zimmer said "no one knows" when asked if Bradford will play again.

"When they went in there, they just cleaned it out," Zimmer said. "It's not bone on bone. There's a lot of good things, but who knows? We didn't expect it would be this long."

Bradford, who will be an unrestricted free agent at the end of the season, led Minnesota to a victory in the season opener over New Orleans by completing 84.3 percent of his passes for 346 yards and three touchdowns.

However, he injured the knee during the game and woke up in pain the next day. He played only one half of one game since then, on Oct. 9 at Chicago when he hobbled around and took four sacks before Keenum came back in to lead the Vikings to a victory.

"It's disappointing," Zimmer said. "The guy worked extremely hard trying to get back, spent a whole bunch of his own money trying everything and it just didn't work out. Hopefully we'll be able to get him back when he gets healthy."

Enter Bridgewater, the 2014 first-round draft pick who was on track to take over as the franchise quarterback after passing for 3,231 yards, 14 touchdowns and nine interceptions while helping the Vikings win the NFC North in 2015. Bridgewater was an injury replacement pick for the Pro Bowl that year.

But then he was hurt dropping back during a routine non-contract drill two weeks before the start of last season, leading to the arduous, lengthy rehab and prompting general manager Rick Spielman to trade first and fourth-round draft picks to Philadelphia for Bradford.

Already a popular player in the locker room, Bridgewater's reputation was further cemented throughout the process of his comeback.

Wide receiver Jarius Wright said the only person he's ever seen as determined as Bridgewater was former teammate Adrian Peterson, who returned from ACL surgery in nine months to start the 2012 opener.

"I know he's going to be great when he gets his opportunity," Wright said. "We all witnessed a miracle."

Zimmer said Bridgewater, who has not played in a non-preseason game in 22 months, will dress for the game this week as Keenum's backup. Rookie Kyle Sloter is also on the roster as the third-stringer. Zimmer declined to speculate about when Bridgewater might become the starter again.

The only victory of the Vikings that Keenum didn't have a hand in was the opener. He's completed 63.9 percent of his passes and thrown seven touchdowns to just three interceptions.

"Whether or not it's Sam or Teddy or whoever else, I've been prepared for these types of situations," Keenum said of the uncertainty of the team's week-to-week decisions on the starter. "Just kind of water off my back."

---

For more AP NFL coverage: http://www.pro32.ap.org and http://www.twitter.com/AP-NFL